Patent GB-615662-A (GB)
Title: Improvements in process timers employing electric discharge devices for electric resistance welding and other purposes
IPC: B23K11/24
Filed: 1946-03-22
Abstract: 615,662. Control systems for resistance welding &c. BRITISH THOMSON - HOUSTON CO., Ltd. March 22, 1946, No. 8926. Convention date, March 27, 1945. [Class 38 (iv)] Relates to a process timer for welding or other purposes and comprising an electromagnetic relay energized through a valve, the control grid potential of which is governed by a timing circuit comprising a capacitor and means adjusting its charging or discharging period. The anode current of one or more such valves is provided from an A.C. source and the timing circuit or circuits are supplied from a unidirectional source of which the voltage is regulated, as by an electro-discharge device of constant voltage characteristic, thereby obtaining constant operation notwithstanding supply line fluctuations. Preferably, the cathode of the valve is connected to the timing circuit through a capacitor and series resistor and a shield grid is connected to the cathode. The relay may be shunted by a capacitor in series with a resistance. The welding control shown has five timing relays 23, 24, 25, 26 connected as set forth, the anodes of the respective timing valves 29, 30, 31, 32, 33 being supplied from an A.C. bus 10 and the timing circuits, comprising timing condensers 45, 77, 54, 64, 72, from a bus 19 which is voltage stabilized by a discharge device 18 and series resistor 17 fed through a rectifier 14. Each timing valve has its cathode connected to the timing circuit through a condenser such as 39 and a resistance 43 and has a shield grid connected directly to its cathode; its control grid is connected between the aforesaid resistance and condenser. The potential of the valve cathodes is determined by resistances 21, 22. Each timing circuit comprises a condenser such as 45 and a charging resistor such as 44. These two being shunted by discharge resistances such as 46, 47, one being adjustable to determine the timing interval. The control system shown operates upon a load circuit 1 which may be the initiating circuit for applying current to a welding load. Welding pressure is under the control of a valve-operating solenoid 2. The valve 30 times the application of heating current to the weld. Its timing condenser 77 is charged from an adjustable 'point on a potentiometer 80 and is discharged through a valve 34, inductance 83 and contact 85 of relay 25. The valve 34 times a cooling period between welding impulses, its control grid being associated with a timing condenser 86 charged through resistance 87 and the contact 89 of the heat timing relay 24 and discharged through resistances 90, 91. With switch 76 closed and switches 60, 61 open, the system is set for pulsation welding. Closure of switch 12 actuates relay 100, whereby pressure is applied to welding electrodes, the charging circuit of the timing condenser 45 of valve 29 is opened and switch 12 short-circuited. After a " squeeze " period, relay 23 opens at 56 the charging circuit of the timing condenser 54 of valve 31 and connects the discharged condenser 86 of valve 34 to its grid. Valve 34 conducts, discharging condenser 77. Relay 24 then operates to close circuit 1 and charge condenser 86, at the same time closing at contact 67 the charging circuit of condenser 64. Valve 34 traverses cut-off and the operation repeats until condenser 54 has discharged to allow valve 31 to conduct, whereupon relay 25 interrupts the anode circuit of valve 34 at contact 85 and welding ceases; contact 66 permits condenser 64 to discharge so that, after a " hold " time, relay 26 operates to open contact 101 and restore the circuits to normal; contact 51 charges condenser 72. Operation of relay 26 interrupts the charging of this condenser so that after an " off " interval relay 27  will operate to interrupt the anode circuit of valve 32 and prevent repetition unless switch 76 has been opened. With switch 61 closed, the relay 25 operates at the same time as relay 23 and only a single pulse is applied to the weld. Switch 60 provides for a change in the range of operation of the timer.